1. Field of the Invention
The present invention relates to a process and a device for the continuous nondestructive control of rails on a railway line by ultrasonics.
2. Description of the Related Art
Devices for continuously controlling rails on a railway line by ultrasonics are described for example in the documents WO/8504485 or U.S. Pat. No. 4,235,112 and they include generally ultrasound emitting--receiving probes in acoustic contact with the upper rail surface as well as an electric device for processing the signals generated by the echoes of the ultrasounds emitted.
One of the major difficulties when controlling rails on a railway line by ultrasonics arises from the need to discriminate between the acoustic reflections or echoes produced by the rail defects which are to be located and identified, and those either generated by specific and normal features of the rail, such as the fishplate holes, the ends of rails, etc, or arising from interferences of an electric or an acoustic nature.
On existing machines, this discrimination can be achieved in two ways:
The signals produced by the ultrasonic probes are displayed, and more generally printed on the chart paper of an all or nothing multitrack reorder, in which the progression of the paper can be controlled by the forward motion of the machine. It is up to the operator to decide from the recording whether a defect was detected or not. This operation can be carried out either in real time by the permanent observation of the recording, or later in the laboratory. PA1 Additional logic inhibition circuits are added to the control system, which are based on the principle that consecutive pulses are counted at given acoustic distances corresponding to the areas in which certain known particular features of the rail can be anticipated. PA1 The first method, based on human judgement, is highly dependent upon the experience and the reliability of the operator, and the results can therefore be highly variable. PA1 The second method is less influenced by personal judgment and is more reliable, but the logic levels are most of the time restricted to simple counts and, therefore, lack flexibility because the algorithms are defined by construction and allow no adaptation in real time by the operator according to the conditions of the rail being controlled. Further, they cannot eliminate completely interfering echoes or signals.
These methods suffer however the following drawbacks:
Further documents are known, i.e. U.S. Pat. No. 3,592,052 and FR 2,244,173, which describe installations for the control of manufactured parts by ultrasonics. These installations are not designed for the control of rails on a railway line, but for the factory control of machined parts or of metal sheets. These installations cannot be adapted to in situ inspections and hence differ fundamentally from our invention.
U.S. Pat. No. 3,592,052 describes an ultrasonic probe which is moved along the part to be controlled and in which the positions of the probe where a maximum echo or no echo is found are identified and measured. This information is then used for calculating the depth of the defect.
French patent 2 244 173 describes the displacement above a part to be controlled of an ultrasonic device designed for identifying areas where the echoes are intercepted by defects. The use of several groups of sensors with different orientations ensures that no defect is overlooked in the control.
None of these installations either are capable of excluding interfering signals and they suffer therefore from the same drawbacks as those mentioned above.